Wednesday, July 17, 2013

A wave of low pressure moving along a frontal system just south of the US border will bring an increasing threat of showers and thunderstorms to southern MB overnight into Thursday morning. Locally heavy downpours are possible with this activity, with rainfall amounts of 15-25 mm possible in some areas. As this precipitation moves out by midday, a trailing cold front will bring the threat of more thunderstorms Thursday afternoon into Thursday evening, especially across southwestern MB. This cold front will mark the leading edge of cooler air that will flood into southern MB Friday into Saturday. Daytime highs Saturday will only be around 20C, with overnight lows likely dipping into the single digits by Sunday morning. Warmer weather is expected to return early next week with highs back in the upper 20s.

At the surface, there will be an inverted trough/dryline connecting the two corresponding lows. Main potential for severe storms will be i) to our SE over Northern Minnesota - where outflow from elevated storms may trigger surface based cells in the warm sector (and where hot, humid conditions and 3000 J/kg SBCAPE will reside), and ii)in SE Saskatchwan and SW Manitoba, associated with the northern low and cold front. The latter is dependent on clearing which NAM hints at (especially south of the TransCanada hwy), but will have to watch for clearing further north where there may be good low level shear locally around the northern low.

18Z NAM is now backing off on keeping a big complex going under the main upper wave Thursday night into Friday morning, which makes sense considering the lack of LLJ..

A high of 38.1C at Beauport QC today with a supposed peak humidex of 51, given a temperature of 37 and a dewpoint of 26 at the time. Seems a tad suspicious to me.. nearby Quebec city (YQB) had a high of 33 with a peak humidex of 43.. so I'm thinking those Beauport readings are inflated.

It's possible rob, but it was SW wind which means the air is warmed the by the big city before reaching Beauport.

Or could the land around be affecting the temperature?

Here is the station:https://maps.google.ca/maps?q=46%C2%B050%2713.000%22+N+%0971%C2%B011%2750.000%22+W&ie=UTF-8&hq=&hnear=0x4cb8be00f4a941c7:0x11df9cd762cd91bb,46%C2%B050%2713.000%22+N+%0971%C2%B011%2750.000%22+W&gl=ca&ei=MZLnUZGaK5SK9gSDyIGoBw&ved=0CCwQ8gEwAA

Rain has pretty much ended for Winnipeg. Some lingering showers over the south part of the city will be moving off over the next hour then we should be dry for awhile, before another chance of showers and thunderstorms later today into this evening as a cold front slips through.

By the way some impressive rainfall totals overnight south of us along the US border with 25 to 35 mm over southern RRV, and 75 to 80 mm over SW MB from Melita through the Turtle Mtn area.

Keeping an eye for potential severe thunderstorms over western RRV and SW MB as cold front comes through this afternoon tapping an area of elevated CAPE. We have some partial clearing through the area which will help with some daytime heating and instability. Timing of storm initiation will dictate if they get close to Winnipeg, or stay mainly to our south and west.

Yeah, it's possible their elevated temps are due to a wind across the city. But there's also a station in Quebec city at the University of Laval, and they also only hit 33C yesterday with a max dewpoint of 23C, so the 37/26 at Beauport seems a bit anamolous.

Things have remained capped so far off to our south.. while convection to our NW is ongoing. HRRR brings in this area into Winnipeg by about 10-11 PM, but weakens it. This makes sense since LLJ will be focused over the Great Lakes region overnite.

On a different topic.. this story regarding the humidex caught my attention..

Unfortunately it largely reflects the public confusion regarding the topic and does not mention specifically the heat index, which is widely used in the US. The heat index takes into account other factors such as wind speed, and produces more realistic values.

According to the radar replay, looks like the WHOLE entire city this time go heavy rain and gusty winds. Rob, when the winds picked up, the ragged low clouds at the front of the storm were moving VERY fast. Is that an indication that the winds are quite a bit stronger than just above the surface!!

Do we know what wind gusts and rain amounts were in different parts of the city yesterday? I'm in Amber Trails, in the northwest, and it was really pretty intense. Wasn't expecting it to be like that at all.

Winnipeg airport had 15 mm of rain during the storm and a peak wind gust of 65 km/h. The Forks picked up 18 mm. That's a lot of rain within 20 minutes. I had about 10 mm in Charleswood during the storm with a peak rainfall rate of 159 mm/hr at 9:21 pm.

As intense as it was, the storm didn't reach severe criteria which is why watches or warnings were not issued for the city. Severe thunderstorms are defined as having wind gusts of 90 km/h or more, hail 2 cm or larger, or rainfall of 50 mm or more in an hour or less.

Is it possible that frogs fell from the sky yesterday? This morning we have about 30 small frogs in one of our window wells, yet there's no water in it so they couldn't have been born there... There's tons in our garden and their croaking was louder than I ever heard last night around 1am

Some close lightning strikes tonight with quite a bit of lightning from several thunderstorm cells that passed over the city this evening. I picked up 22 mm of rain today, most of it with thunderstorms this evening

I've had to replace the forecast graphic on my main webpage from the CBC to CTV. CBC forecast graphic has been completely out to lunch on the weekends, and even this morning it was advertising temps of 27-28C all week when we won't be above 25C until maybe next Sunday or Monday. CBC graphic seems to be randomly generated on the weekends with some rather bizzare forecasts.

Regardless, clicking on the icon gives you EC's forecast. I'd prefer to have an EC forecast graphic icon, but they don't have one that shows the 7 day forecast all at once. As a result, I'm forced to display the 7 day forecast graphic from one of Winnipeg's TV stations instead.